Centrifugal fans



June 29, 1965 c. o. woon CENTRIFUGAL FANS Filed D60. 51. 1963 Iaavezzoab WZ 0. uod, 'yw aww United States Patent() 3,191,851 Y CEN TREUGAL FANS Carl 0. Wood, Needham Heights, Mass., assgnor to Westnghouse Electric Corporation, Pittsburgh, Pa., a corporation of Pennsylvania Filed Dee. 31, 1963, Ser. No. 334,771 Claims. (Cl. 23m-127) This invention relates to centrifugal fans, and relates more particularly to centrifugal fans having so-called half cut-offs.

A conventional centrifugal fan usually has a scrollshaped casing with a tangential air outlet between its front and back walls. The front wall forms an air inlet passage converging towards the fan rotor, the latter having a side plate forming an air inlet passage converging towards and terminating adjacent to the inner end of the rst mentioned passage. Such passages usually occupy about one-half of the space between the front and back walls of the casing, with the fan rotor being close to the back wall, and occupying about the other half of the space between the front and back walls. Since the air outlet extends the full width of the space between the front and back walls, the fan rotor discharges directly into one-half the width of the outlet, and indirectly into the other half of the width of the outlet. Such a fan usually has a cut-off sheet which continues the curvature of the casing, and which extends into and across the width of the fan outlet passage from 10% to 40% as explained and shown on page 1949 of Marks Handbook,

fourth edition, published by McGraw-Hill Book Co., for converting rotary ilow into linear flow. While such a cut-oil:` sheet improves the pressure characteristic of such a fan at loads below maximum volume loads, since it extends partially into the fan outlet passage, it partially blocks such passage, and for such a fan designed to operate at or near maximum output, a half cut-off sheet is used behind the two inlet passages only so as not to protrude into the outlet passage behind the fan rotor.

Due to such a fan rotor discharging into an outlet passage having about twice the width of the rotor, with one-half of the outlet passage being offset from the space behind the rotor, there is a mismatch of impedance between the rotorA and the outlet passage, and discontinuity of flow, resulting in turbulence, noise and loss in efficiency, such turbulence being greatly increased in the outlet passages of fans having half cut-olf sheets only, since there is spinning air leaving the fan rotors and entering the outlet passages.

lThis invention provides in such an outlet passage behind the two air inlet passages, a fairing which blocks that portion of the outlet passage which is not directly behind the fan rotor, for decreasing discontinuity of flow and reducing noise at the fan outlet.

An object of this invention is to reduce the noise at the outlet of a centrifugal fan.

Another object of this invention is to increase the eiciency of a centrifugal fan.

This invention will now be described with reference to the annexed drawings, of which:

FIG. l is a side view, partially in section, of a centrifugal fan embodying this invention, and

FIG. 2 is a section along the lines 2 2 of FIG. 1.

Scroll-shaped casing 10 has a front wall 11 and a back wall 12. A conventional fan rotor 13 is supported for `rotation on shaft 14 within the casing. Flared wall 9 attached to the front wall 11 around an opening therein, forms an air inlet passage which converges towards the rotor 13. The latter has a ared side plate 16 which forms an air inlet passage which converges towards and terminates closely adjacent to the inner end of the passage 15. The rotor 13 has a back plate 18 closely adjacent to the back wall 12 of the casing. The casing has an air outlet passage 19 extending between the walls 11 and 12. A half cut-off sheet 20 is attached at its outer end to the casing by rivets 22, and is attached at its inner end to the casing by a rod 23 around which its inner end is rolled. and which extends between the walls, 11 and 12.

The construction described so far in connection with the drawings is conventional. This invention adds, preferably in a short duct attached to the casing at the fan outlet and forming an extension of and part of the outlet passage 19, a stream-lining fairing 30 having a flat side in contact with front wall 31 of the duct 25, which front wall forms a continuation of the front wall 11. The fairing has a rounded nose 32 which faces the cut-off sheet 20, and has a tip 33 at the wall 31. The fairing 30 extends into the duct 25 behind the cut-off sheet 20, about the width of the latter, which width is about equal to the combined widths of the two inlet passages of the fan, and preferably extends between top and bottom walls" 34 and 35 respectively, of the duct 25. The fairing 30 has a perforated cover sheet 38 around brous sound absorbing material such, for example, as ibre glass.

The fairing 30 by reducing the width of the outlet passage of the fan to substantially that of the space directly behind the rotor 13, reduces discontinuity of ow; increases efficiency, and reduces noise at the fan outlet. The fairing also absorbs noise resulting from turbulence directly behind the fan rotor, and caused, in the illustrated fan, by lack of a cut-off sheet behind the fan rotor. The fairing also reflects noise back into the fan where it is transformed into heat.

What is claimed is:

1. In a centrifugal fan having a scroll-shaped casing, having a rotor supported for rotation within said casing, said casing having an air inlet opening, and having a wall forming an air inlet passage converging from said opening towards said rotor, said rotor having a side plate around an air inlet passage converging towards and terminating adjacent to the inner end of said rst mentioned passage, said casing having an outlet passage with a width equal to the combined widths of said inlet passages and of said rotor, the combination therewith of a streamlining fairing extending into said outlet passage behind said inlet passages only.

2. The invention claimed in claim 1 in which said fairing has a perforated surface facing that portion of said outlet passage that is directly behind said rotor, and in which said fairing encloses sound absorbing means.

3. The invention claimed in claim 2 in which said casing includes a half-cut-olf sheet behind said inlet passages only.

4. The invention claimed in claim 1 in which said casing includes a half-cut-oif sheet behind said inlet passages only.

5. In a centrifugal fan having a scroll-shaped casing, having a rotor supported for rotation within said casing, said casing having a front and a back wall, said front wall having an air inlet opening, having an inlet passage converging from said opening towards said rotor, said rotor havin a side plate around an air inlet passage converging towards and terminating adjacent to the inner end of said first mentioned passage, said rotor having a back plate adjacent to said back wall, said casing having a tangential air outlet extending between said walls, the combination of a short duct connected to said casing across said outlet, and a streamlining fairing extending into said duct behind said inlet passages only, said fairing having a rounded nose facing said outlet.

6. The invention claimed in claim 5 in which said fairing has a perforated surface facing that portion of s. the passage within said duct that is directly behind said rotor, and contains sound absorbing means.

7. The invention claimed in claim 6 in which said casing has a half cut-oit sheet between said nose and said outlet.

8. The invention claimed in claim 5 in which said casing was a half cut-of sheet between said nose and said outlet.

9. In a centrifugal fan having a scroll-shaped casing, having a rotor supported for rotation within said casing, said casing having an air inlet opening, and having a wall forming an air inlet passage converging from said openin towards said rotor, said rotor having a side plate around an air inlet passage converging from said rotor towards and terminating adjacent to said first mentioned passage, said casing having an air outlet passage with a width equal to the combined widths of said inlet passages and of said rotor, the combination of means extending into said outlet passage behind said inlet passages only for reducing the width of said outlet passage to substantially the width of said rotor.

10. The invention claimed in claim 9 in which said casing is provided with a half cut-off sheet between said inlet passages and said means.

References Cited by the Examiner UNITED STATES PATENTS 2,107,897 2/38 McMahan 230-127 2,126,230 8/38 TroXell 230-127 2,134,142 10/38 Orear 230-127 2,160,666 5/39 McMahan 230--127 2,285,976 6/42 Hintson 230-114 2,452,274 10/48 Walters 230-128 2,841,326 7/58 Davis 230-114 2,987,983 6/61 Solzman 230-232 3,085,741 4/63 Burkhardt 230-127 FORETGN PATENTS 285,815 5/28 Great Britain.

KARL I. ALBRECHT, Primary Examiner. 

1. IN A CENTRIFUGAL FAN HAVING A SCROLL-SHAPED CASING, HAVING A ROTOR SUPPORTED FOR ROTATION WITHIN SAID CASING, SAID CASING HAVING AN AIR INLET OPENING, AND HAVING A WALL FORMING AN AIR INLET PASSAGE CONVERGING FROM SAID OPENING TOWARDS SAID ROTOR, SAID ROTOR HAVING A SIDE PLATE AROUND AN AIR INLET PASSAGE CONVERGING TOWARDS AND TERMINATING ADJACENT TO THE INNER END OF SAID FIRST MENTIONED PASSAGE, SAID CASING HAVING AN OUTER PASSAGE WITH A WIDTH EQUAL TO THE COMBINED WIDTHS OF SAID INLET PASSAGES AND OF SAID ROTOR, THE COMBINATION THEREWITH OF A STREAMLINING FAIRING EXTENDING INTO SAID OUTER PASSAGE BEHIND SAID INLET PASSAGE ONLY. 